I was watching 14 - Diaries of the Great War in which the journalist Charles Edward Montague chaperons a MP through the trenches to show him the realities of the war. The impression that I got was that the British military command needed to get the support from the parliament in order to secure more men and weapons to continue the war.
This made me wonder, in England, Germany and France which actor(s) was the main proponent for a continuation of a war instead of negotiating for peace or surrendering. Was it the military high command that pressed on or was it the respective governments that wanted to continue the war effort?
Not sure if this answers what you want, but here goes:
Gavrilo Princip was seen as a Yugoslav nationalist (1) that threatening the imperial throne of Austria-Hungary. Therefore, by taking action against Serbia, A-H was not only striking a blow against Serbia, but lashing out against those who would see the monarchies and empires of Europe unseated. By In July of 1914, Kaiser Wilhelm informed A-H that it could count on Germany's "faithful support" (2) in an effort against Serbia. Essentially, the Kaiser offered A-H military support without fully considering the ramifications of this decision, throwing the full might of the German war machine into a localized conflict that would soon turn into a massive war.
When the Kaiser voiced his support for A-H in their effort against Serbia, he erroneously assumed that Russia would support Germany and A-H for two reasons. The first was that the Kaiser and the Tsar Nicholas II were in fact related. In private correspondence they enjoyed a very friendly relationship. However, the Kaiser also assumed that the Tsar would throw his support behind the empires of Europe against a nationalist assassin, as Tsar Nicholas II (and other public officials) had been assassinated during the 1880s and 1890s. One of the reasons the war dragged on as long as it did can be found in Russian political thought from the late 1800s. Panslavism was a theory that imagined a union of all Slavic people under a mother state (read: Russia). By this theory, Russia could not ignore the call of a Yugoslav nationalist (a Slav) calling for help. Interestingly enough, on the other side of the conflict, Kaiser Wilhelm hated Slavs, fueling not only a political motivation for war, but also another one based on his own convictions. With the entrance of the Russia into the war, it became a personal conflict for the Kaiser.
In conclusion, the continuation of the conflict was partially because of the fateful telegram that the Kaiser issued A-H offering German military support and the incorrect assumption that Russia would side with Germany and A-H against Serbia. Sources:
1: http://en.wikipedia.org/wiki/Gavrilo_Princip
2: Why Nations Go to War Third Edition, John G. Stoessinger